Hooded exhaust system



May 31, 1960 G. B. GERRISH Hoonsn EXHAUST SYSTEM 2 Sheets-Sheet l Filed Oct. 17. 1958 HUMA L HUMVMUUUJ May 31, 1,960 G. B. GERRIsH Hoonsn EXHAUST SYSTEM 2 Sheets-Sheet 2 Filed Oct. 17, 1958 Iii! vnited States L, 2,93 8,714 HOODED EXHAUST SYSTEM Grenville B. Gerrish, Melrose, Mass., assigner to *Wol- This invention relates to the exhausting of undesirable products of combustion or other heated* gases from local drying or heat generating areas located within larger plant areas. This application is a continuation-in-part of my earlier copending application Serial No. 627,361, filed December 10, 1956 and now abandoned.

Serious'diculties are often presented by irregularities in air circulation and air consumption inevitably resulting from the introduction of equipment which, for comfort, safety, or other reasons, must be hooded or otherwise connected to an exhaust leading outside the air condi tioned area. In case of oxygen consuming equipment, such as ame heaters, a considerable load may be placed upon the air supply for the area. This problem is aggravated by the practice of exhausting air to reduce due gas temperatures and to prevent the gases from escaping into the area. If replacement air is supplied by leakage or direct entry from the outside atmosphere, a considerable load will be placed in cold Weather, upon the normal inside heating equipment or in warmer weather upon the normal inside air conditioning unit. Also undesirable drafts will be created regardless of the outside temperature. The air conditioning and heating installations cannot readily be changed for optimum operation if machine locations are changed or additional air consuming units are installed in the general area. The amount of make-up air supplied is a very significant factor in the cost of installing and operating heating and air conditioning systems and is therefore usually kept to a minimum.

Another diiculty arising from attempts to supply air consuming equipment With air from a confined area is that the equipment will tend to operate at dierent temperature levels depending upon the temperature of the ambient air. For example, if a Window is opened in Winter, through which air ows to a heat treating unit, such as a furnace, baker or oven, the unit will tend to operate at a lower temperature level and thus non-uniform cooking, drying or other heating of the product being treated may result. Increased fuel consumption will certainly result if the operation is under automatic control. To further complicate matters, many processes operate more eiiciently with air at a temperature above the normal comfort conditions maintained in the general area.

It is therefore an object of this invention to provide an air supply to an individual, or group of individual, air attracting units within a localized area of a general plant space, which supply is dependent on the general space air supply and is so controlled with respect to the air demand of the unit that the unit will operate without drawing on or spilling air into the general area.

It is another object of this invention to supply replacement air at a selected temperature having a lower limit determined by the maximum temperature of the outside source of air and an upper limit determined by the amount of heat liberated by the equipment or process involved.

Since auxiliary air according to my invention is obtained from outside the general area, and preferably from outside the plant or other confined space, I encounter the problem of the outside air temperature being non-uniform. Hence I incorporate in my system means for preheating the intake of outside air to a temperature at 2,938,714 Patented May 31, 1960 which the equipment is adapted to operate most eliiciently. Such temperature is maintained regardless of the outside temperature (within reasonable limits), so that the equipment will produce accurate and uniform results. This is of considerable importance where exact time temperature exposures of products are essential, as they usually are for plastic cures. Also considerable fuel is saved by the recapturing of a portion of the heat in the exhaust gases which would otherwise be wasted.

Accordingly, a still further object of my invention is to provide in such auxiliary air supply apparatus, means for insuring that, regardless of the temperature of the outside air within reasonable limits, the temperature of the air fed to the air consuming equipment or unit shall remain reasonably constant.

I have further found that when such preheating is provided not from an independent outside source, but from a heat exchanger coupled with the unit exhaust system, a balanced intake and exhaust can be maintained so as not to effect, other than by radiation and product heat, the general area air supply, regardless of variations in the outside air temperature. The result is that once the desired amount of air ow through the unit has been provided for, there is no need to adjust the intake or exhaust, assuming a constant rate of heat generation by the unit. The reason lies in the heat exchanger wherein heat is transferred to the incoming air. If there is a constant volume of air input, such as can be obtained with a fan and damper arrangement adjusted so that the fan will impel say 10,2000 cubic feet per minute into the system; and if the same weight of air is exhausted as is taken in, through the use for example of another constant volume fan and damper arrangement, the desired balanceV will obtain even though the volume of exhaust air moved by the other fan must be substantially larger (say 13,500 cubic feet per minute) to take account of the expansion of the exhaust air that has taken place as a result of the heat generated in the unit and absorbed by the exhaust air. This is true in spite of the fact that the weight of air taken in varies according to its temperature because the heat gain and the heat loss in the exchanger are equal. In practice the weight of exhausted products of combustion is also taken into account but this is relatively small. The excess of air in the exhaust caused by changes in resistance to flow of air in the heat ex` changer ducts when the temperature of the intake drops, is so small (approximately 6 percent maximum under extreme winter conditions) that it has been disregarded.

The novel features of the invention, together with further objects and advantages thereof, will become apparent from the following detailed description and thedrawings to which it refers.

In the drawings:

Fig. 1 is a view in elevation of the hooded exhaust system according to the invention with portions broken away to show certain parts more clearly; and

Figs. 2 and 3 are sectionalviews taken on lines 2 2 and 3 3, respectively, of Fig. l.

With reference now to the drawings, it will be observed that the exhaust system according to the invention includes an inner hood 11 and an outer hood 12. Structural members, such as 13, are provided to support .the hoods above a unit 14 which is the source of the hot gases to be exhausted. By way of example, there has been illustrated a heat-curing unit for products 15, including a conveyor 16 to transport them. 'I'he unit rests on the lloor 17 of a plant area or the like ,which also provides a footing for the member 13. As shown, the inner hood comes down to approximately the level of the conveyor while the outer hood extends somewhat lower, but still substantially above the level of the licor.

Disposed in the stream of the hot gases at what might be termed the throat of the inner hood is a heat exchanger 21, defined exteriorly by walls 22 through 25. These walls form a chamber which leads from the hood toan exhaust duct 26. The exhaust `duct in turn passes through the roof 27 ofthe plant or other structure Whereinthe unit isV located. There is an axial fan 2S mounted within the section of the exhaust ductwork that extends above the roof and there is a damperH 29'Lnear thev inlet end thereof to vcontrol the flow of air. Fan 28 is-driven by a motor 28.

The'heat exchanger includes, in addition tothe cham-v ber-dening walls, 22-25, a series ofrectangular tubes 31. Thev tubes are arranged side-by-side; with' their broader ,walls adjacent one anothenrthat is, effectively on end, so that the hot gases, in` order to escape, must pass between'them, The tubes themselves communicate between a transistional ductl section 32` andY the part'of the regionbetween the inner and outer hoods which islocated above an air distribution baille 30. Specically the tubes discharge into the upper partof this region Where it occupies the largest volume, owing to the fact thatthe upper portion inner hood 11.. is.y necked down. Discharging into .this same. mixing region adv jacent the tubes 31 are ducts 33 and 34. leading from a point adjacent the inlet end of the duct section 32 and passingy around onV opposite sides of the heat exchanger. At a common junction, duct section 32, andV ducts 33, 34v are connected to an inlet duct 35, whichV communicates with the out-side atmosphere through the roofY 27. A fan- 36 is provided to draw iair from the atmosphere into the ductV 35 and. a motor 36 serves` to drive this fan. There is also ai damper 38 in the duct 35 near theV pointwhere it joins the ducts 33, 34 and the duct section 32 in order to control the ow of air to the latter. To'apportion the ilow between the duct section 32- on the-one hand and the ducts 33 and 34 on the other, there are provided dempers `41 and 42. When dampers 41 4are closed, they seal oi the mouth of the duct section 32 leading to the heat exchanger tubes 31. When dampery 42 is closed, it seals'off the mouth ofA ducts 33, 34 which provide a direct pathV to the region between the hoods. Dampers 41 and 42 are adapted to operate in tandeml by means of control-arms 43, and 44, respectively, joined to a common actuating member 45. Accordingly, these dampers provide a ready means forcontrolling the temperature of the intake` air and preferably they are arranged to be operated by a posi'- tional control motor (not shown) which responds automatically to changes in temperature offthe blended air blown into the hood region between the inner and outer hoods.

' The reason for creating a substantial pressure throughout lthe fresh air inlet system is to insure that fresh make-up air does not become contaminated' by the hot exhaust gases. This pressure, coupled with the partial vacuum in the hood created by the exhaust fan, insures that any leak inthe tubes will result in fresh air being blown out of them rather than toxic gases entering.

In operation, let it be assumed firstY that the dempers 41V are completely closed and the damper 42 is open. As a consequence,l all the fresh air drawn in by the intake. fan bypasses the heat exchanger and enters the space between the inner and outer hoods by way of the ducts 33 and 34. From there it is sucked' up through the inner hood, passed aroundY the source of heat 14, and expelled through the roof by the exhaust fan. YItv vthe temperature of the outsidegaii decreases and if the intake fan has a constant volume characteristic, assuming-for the moment that damper 41 is kept closed, the weight. of air drawnY in by the -fanV 36 will increase. However, there will be a like decrease in the temperature of the exhaust air, and a` like increase in the weight of, expelled by the exhaust fan, so that the system 4. remains in balance. Now if the dampers 41 and 42 are adjusted to cause some of the inlet air to -ow through the heat exchanger, the temperature of the air entering the inner hood will increase. That is to say, the air heated by the heatvexchangervwill mixwith the unheated air passed by the ducts, producin'gha'net tempera-v ture. rise. This will not change the balance between the weight of air drawn in and the weigpht'ofY air expelled from'the system, since the amount of heat transferred to the incomingair is substantially equal to that extracted from the exhaust Accordingly, conventional'fansand impellers of iixed constant volume rating can .-beemployed, and the dampers 41 and 42 adjusted at will, without disturbing the balance between intake and exhaust.V The same is true, of course, if these dampers are adjusted automatically so as to maintain constant the temperature of the air entering thev inner hood. This` being so, once the systemhas been balanced, at no time dores-the system draw upon or expel airinto the surrounding plant area.

Although the invention has been described in connection with a single preferredY embodiment, those skilled in the art will appreciate that this-embodiment can-be modied in Various ways without departing frornjthe spirit and scope of theinvention. Therefore the invention should not be deemed to be limited to the details of what has been described herein, but rather it should be deemed to be limited only by theY scope of the appended claim.

What is claimed is:

An air conservation system for aV large confined space having arelatively small air attractingunit in a localized area in con-etant communication in normal'op'eration of the unit with the large con'ned space, comprising a double-Walled hood overlying the localized areaof the air attracting unit, the inner hood encompassingV the area of air exhaustion from said unit, an exhaust'duct leading from said inner hood, an exhaust fan in said exhaust duct, heat exchanger tubes interposed between said inner hood andsaid exhaust duct, the outer hood encompassing an area surrounding ysaid rst hood, an air intake duct leadingfrom a source of air supply outside of' saidconned space to said heat exchanger vtubes and communicating beyond said exchanger with the space between the double'walls of said hood, a bypass from said intake around said heat exchanger tubes, afan in said. intake, means in saidintake duct and means in said exhaust duct whichl are preset in relation to each other for controlling the rate of gas How induced by operation of said fans in said intake and exhaust ducts to supply air from said intake to saidl unit ata rate byY weight which, when added to the weight of any gas products originating in said unit is substantially equivalent to the rate by weight of gas expelled through said exhaust duct by said exhaust fan to prevent air in the large confined space fromv entering the `air attracting unit and to prevent air in the air attracting unit from entering the large coniined space, damper means disposed in the paths of the air which passes through said heat exchanger tubes and bypass, and means to move said damper means synchronously in opposite senses to selectively apportion the air which passes through said exchanger tubes and bypass respectively without aiecting the amount of air flow induced by said` fans in said intake and exhaust.

References Cited in the le of this patent UNITED STATES PATENTS 1,582,892 Beadle Mayr4, v1926 2,072,833 Baird et al. Mar. 2, 1,937 2,355,671 NaeherV et al. Aug. 125, 1944 2,521,866 Ott Sept. 12, 1950 FOREIGN PATENTS 393,378 Gr'eat Britain ---t June 8, 1933 

